The goals of the present proposal are twofold: 1. to continue to develop and refine parent report and observational assessment techniques for measuring infant temperament and caretakers socialization of temperament-related behavior; and 2. to use these assessment instruments in the execution of a short-term longitudinal study of infant temperament at 3-, 6-, 9- and 12-months of age are now being developed and cross-validated against observational measures of temperament on a sample of 50 subjects. Observational measures are based on sequential coding of temperament-related behavior in the home and in the laboratory during administration of Bayley Mental and Motor Scales. During the first year of the proposed research, we plan to develop, refine and evaluate similar observational and caretaker report measures of temperament for 18-month old children. We then propose to carry out a short-term longitudinal study of infant temperament during the second and third years of the project. In the longitudinal project parent report instruments will be collected for two cohorts of 50 children each at 3-, 6-, 9-, 12-, and 18-months of age. In addition, infants will be observed in the home and in the laboratory at 6-, 9- and 18-months of age, and 18-month-old children will be observed during peer interaction. The longitudinal study will allow further cross-validation of our measures. In addition, individual differences, developmental trends, and interactions between children's temperament and caretaker socialization of temperament-related behavior will be examined, and sex difference, age, and birth order analyses will be performed.